How to create an Xbox Arena tournament on Xbox One or Windows 10

Xbox Arena tournaments are here, and they are extremely easy to create!
Xbox Arena is a system that allows users to create their very own tournaments complete with notifications, scheduling, and more. The feature is rolling out more broadly as part of the July 2017 Xbox update, after being in testing for several weeks on the Xbox Insider program.
If you want to create your very own tournament, you'll have to follow these steps!